The present invention relates to a unit of the type used in treating a substance, such as printing ink, paint, coating resins of various compositions or the like, which contains an ultraviolet-sensitive compound to effect rapid setting or curing of the substance when subjected to ultraviolet radiation after being applied as a coating to a substrate such as an article made of paper, metal, plastic or other material. More particularly, the invention relates to a unit including at least one lamp such as a mercury vapor lamp designed to produce ultraviolet radiation when energized and having a curved reflector mounted within the lamp housing behind the lamp to reflect the radiation from the lamp out of the housing and onto the coated substrate which may be located below the housing. Units of this general character are disclosed in U.S. Pat. Nos. 3,829,982; 3,826,014; 3,745,307; 3,733,709 and 3,159,464.
In treating a substance containing an ultraviolet-sensitive compound, the degree to which the substance is cured upon being subjected to the ultraviolet radiation depends upon the intensity of the ultraviolet radiation applied to the substance and the length of time which the radiation is applied. Thus, for a higher intensity of ultraviolet radiation, less time is required to achieve the same degree of curing than for a lower intensity of ultraviolet radiation. Further, the higher intensity radiation provides relatively greater absorption into the interior of the substance and thereby allows relatively thicker coatings or relatively less ultraviolet sensitive coatings of identical thickness to be cured. Examples of these less sensitive coatings are coatings to which pigments have been added; with black pigments commonly producing the greatest deterioration in ultraviolet light sensitivity. One system presently used to cure ultraviolet sensitive coatings employs a long-arc ultraviolet lamp with an elliptical reflector. This system, however, has proved to be unsatisfactory when high intensity levels are required since the intensity at the substrate in such a system is normally less than 1.2 watts .times. F/mm.sup.2 (F representing an efficiency factor defined in the table shown hereinafter).
A primary objective of the present invention is to provide a new and improved unit of the foregoing general character for concentrating the ultraviolet radiation emitted from the lamp into a small area of high intensity on the coated substrate so as to make more efficient utilization of the ultraviolet radiation emitted from the lamp, thereby reducing the time required for curing an equivalent thickness of coated substrate or for achieving a cure of thicker and less sensitive coatings at an equivalent time.
A more detailed object is to achieve the foregoing by constructing the unit so that the ultraviolet radiation from the unit strikes the coated substrate at spaced locations along the width thereof with high intensity beams, complete coverage of the width of the substrate being achieved through the use of a cluster of similar units whose emitted beams strike the substrate at staggered positions with respect to the beams of other units thereby subjecting the entire width of the coating to a uniform high intensity radiation as collectively emitted from the cluster.
An additional object is to construct the cluster of units so that the staggered beams from the units strike the substrate coating in an overlapping manner by a significant percentage to enable selective adjustment in the intensity of the radiation striking the coating to be achieved by de-energizing, either partially or completely selected lamps within each array.
A still further object is to produce the high intensity beams of ultraviolet radiation through the use of an array of short-arc ultraviolet lamps in each unit with the emitted radiation of each lamp being separately controlled to enable selective adjustment in the intensity of the radiation striking the coated substrate.
Another object of the present invention is to provide a unit in which the intensity of the ultraviolet radiation striking the coated substrate may be adjusted selectively for substances of differing ultraviolet sensitivity to that intensity which more efficiently cures the coating on the substrate.
A more detailed object is to apply high intensity ultraviolet radiation to the substrate coating by concentrating the radiation emitted from each of the lamps in said array through the use of a pair of reflectors associated with each lamp to first collimate the radiation emitted from the lamp in a beam and, thereafter, to reflect the collimated beam toward the substrate in such manner that the rays of the beam are focused upon the substrate coating so that the intensity of the ultraviolet radiation striking the coating is increased substantially over the intensity of the radiation in the collimated beam.
The invention also resides in the novel construction of the unit wherein each pair of reflectors comprises a paraboloidal reflector and a concave spherical reflector and wherein the short-arc lamp is located adjacent the paraboloidal reflector with the arc of the lamp positioned substantially at the focus of said reflector so that radiation from the lamp is reflected from the paraboloidal reflector in a collimated beam toward the spherical reflector which in turn, reflects and focuses said beam on the coated substrate to provide a magnified image of the object lamp arc by a ratio equal to the ratio of the focal length of the spherical reflector to the focal length of the paraboloidal reflector. Said magnified arc image area can be varied by changing the focal lengths of either the spherical reflector or the paraboloidal reflector or both to thereby change the ratio of their focal lengths and in turn the arc image area on the coated substrate.
Still further, the invention resides in the novel manner of mounting the spherical reflector in the unit for movement between a first position reflecting the collimated beam toward the coated substrate and a second position reflecting the collimated beam in another direction so as to avoid prolonged application of ultraviolet radiation to the coating in the event movement of the substrate should be halted beneath the unit.
In addition, the invention resides in the novel manner of cooling the reflectors and the lamps within each array during use.
These and other objects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.